2002 Ranger, 2.3L engine, 60,000 miles. As I'm driving down the Interstate the check engine light comes on again. I've got the Actron scanner handy because it's just did this the day before, and I plugged it in to reset the P1432 code. I looked at the "vehicle" data while driving and saw that my coolant temperature was 260 degrees even though the dash guage showed "normal" temperature.

Next day I changed the thermostat ($120.00 thermostat with an electrical plug on it), filled it and tested it, got the same thing, Dash guage showing normal, Actron showing above 250 degrees Farenheit and lower hose between thermostat and radiator cold. I used an infrared thermometer to view the hose temperatures, the top hoses, including to the Overfill/fill tank were very warm, but the lower hose was as cool as the outside air.

Took thermostat back, got different one (same brand) and tried that. Same thing. Took Truck to local shop and told story.

They called back, looking into what might be the cause. Said something about the thermostat being electrically controlled by the line that plugged into it. I thought that line was a "temperature" monitoring line, but it looked fine, the plug was good, not burned or frayed where I could see it. Dash guage appeared to work, moved from cold to normal, but never moved above that level even as the Actron showed the coolant temperature rapidly building.

I wondered if anyone had experienced this, and could suggest anything to fix it. I don't want to remove the thermostat all together, but it seems illogical that two thermostats were bad (not including my original). I don't know about the "electronic controlled thermostat", is that a possibility? I dropped it at the shop shortly before they closed so their preliminary diagnosis was just that, I'm sure they'll look at it more thoroughly, but I want to have some idea what to expect when they call, or a place to point them in case they don't have a quick answer.

I wondered if anyone with a 2002 Ranger and an Actron Scanner could check their vehicles coolant temperature and let me know what they get.

Seems no one is certain what's happening to mine, or why it shows such a high temperature on the Actron. I'm not convinced that this is normal, or that the temperature sensor which is read on the Actron should be this high. The Dash guage reads normal and it rose no higher than around 260 pn the Actron so the thermostat must have opened at that temperature or it would have gone sky high.

I was able to remove the thermostat from the old assembly and drive it 150 miles home, and the Actron showed 153 degrees during the trip. I also got a code once telling me the temperature was too low.

I'm beginning to suspect that the temperature shown on the Actron is not the actual coolant temperature, and that the location of the sensor might cause this to read this high. If anyone with this truck can check theirs, it might confirm or rule out this theory. I"d appreciate it.

I'm stumped, and the mechanics are stumped. They're ready to remove the radiator, and/or the waterpump even though with the thermostat removed it adequately cooled. No-one knows why this is showing so high, nor why the lower hose never seems to get warm.

I have a 2002 Ranger 2.3L doing exactly the same thing. I changed the thermostat but the lower radiator hose is still cold after the truck has heated up. 2 other points though, my compressor is cycling on and off when I turn on the heater (even though I am not turning on defrost) and I appear to be having a head gasket leak (shop says there is exhaust in my coolant). I am trying to figure out what all is going on before repairs nickle and dime me what the truck is worth. Anyone, please help if you can.

I realize these are old posts but mine is doing this also.
I thought it was just a wrong reading from the Cylinder Head Temp Sensor, but today coolant came out of the overflow.
Did you guys ever figure this out?

I have a 2002 Ranger with 140K and the thermostat had done a poor job at controlling temp for the past year or more. Call me cheap but I just replaced the stock one having the electric heater with one from a 2004+ Ranger without the heater. I ordered a 194°F Stant and it fit perfectly. Upoin examining the old one I discovered that the seal on the sliding valve had torn which explains why it heated so slowly. The electric heater had broken. To fool the computer I connected a 1200 Ohm 1/4 Watt resistor across the leads to the connector. The CEL is staying OFF and the temperature now controls correctly. I figure I saved ~$100 and now drive a later model!

i'm glad i found this post,i did nickle and dime it with new clutchfan,waterpump and a couple of thermostats.ford must have realized this was not working and went back full manual.going to buy a 2004 thermostat today.still wondering if i will be able to read temp on guage or is the thermostat connector strictly for pcm control